Direct observation of the specific heat of Majorana quasiparticles in superfluid3He-B

Yu M Bunkov,R R Gazizulin

doi:10.1038/s41598-020-77128-5

Abstract

The existence of Majorana quasiparticles was predicted in the edge state in topological insulators, especially in the p-wave superfluid medium {^3}He-B. Due to its purity and coherent quantum state, {^3}He-B is an ideal platform for searching for Majorana fermions in condensed matter systems. In the limit of extremely low temperatures, the density of Bogolyubov quasiparticles and the heat capacity of {^3}He-B decrease exponentially. In this article, we present the first observation of the deviation of its heat capacity from exponential dependence in the limit of record low cooling. We found an additional heat capacity that more than doubled the heat capacity of bulk {^3}He-B and changes as T^2. The additional heat capacity is in good agreement with the predicted heat capacity of 2D gas of Majorana. This observation is a direct proof of the existence of Majorana quasiparticles in {^3}He-B.

Highlights

The existence of Majorana quasiparticles was predicted in the edge state in topological insulators, especially in the p-wave superfluid medium 3He-B
No one has discovered an elementary particle corresponding to the Majorana fermion, there are quasiparticles in some special classes of condensed matter systems that must have Majorana properties[2,3,4]
A distinctive feature of this dispersion relation is the absence of excitations with E

Summary

Majorana and Bogolubov QPs heat capasity

A direct consequence of the Bogolyubov QPs energy gap is the exponential decreasing of 3He-B heat capacity with cooling: Cbulk ∼ V kF2 ξ −1. Z is a parameter, related to a roughness of the surface on a characteristic length about few ξ. Parameter Z = 1 for smooth surface and decreases to zero in the case of roughness. The ratio of these heat capacities, including the numerical factors, reads: Scientific Reports | (2020) 10:20120 |. From Eq (3) it can be seen that depending on surface-to-volume ratio Majorana QPs may have significant contribution to the 3 He heat capacity (in comparison with the heat capacity of Bogolyubov QPs) below some low enough temperature. We have measured the heat capacity of 3He-B samples in two cells with very different volume-to-surface ratios at zero pressure as a function of temperature down to about 0.1 mK

Precise heat capacity measurements

The experimental results

The surface of the copper walls after annealing

Additional information